1. Field of the Invention
The present invention relates to current-perpendicular-to-plane (CPP) magnetic detecting elements, and particularly to a magnetic detecting element in which change in product of ΔR and cross sectional area 10 (ΔR·A) can be increased effectively.
2. Description of the Related Art
FIG. 14 is a sectional view of a known spin-valve magnetic detecting element.
The spin-valve magnetic detecting element includes a multilayer laminate 9 essentially composed of an antiferromagnetic layer 2, a pinned magnetic layer 3, nonmagnetic material layer 4, a synthetic ferrimagnetic free magnetic layer 5 including a first free magnetic layer 5a, a nonmagnetic interlayer 5b, and a second free magnetic layer 5C, a nonmagnetic material layer 6, a pinned magnetic layer 7, and antiferromagnetic layer 8, deposited in that order. Electrode layers 1 and 10 are disposed on the upper and lower surfaces of the multilayer laminate 9. Also, a hard bias layer 11 lies at both sides of the free magnetic layer 5, and the hard bias layer 11 is provided with insulating layers 12 and 13 on the upper and lower surfaces thereof.
The antiferromagnetic layers 2 and 8 are formed of PtMn; the pinned magnetic layers 3 and 7 and the first free magnetic layer 5a and the second magnetic layer 5c are formed of CoFe; the nonmagnetic interlayer 5b of the free magnetic layer 5 is formed of Ru; the nonmagnetic material layers 4 and 6 are formed of Cu; the hard bias layer 11 is a hard magnetic material such as CoPt; the insulating layers 12 and 13 are formed of alumina; and the electrode layers 1 and 10 are formed of a conductive material such as Cr.
The magnetic detecting element shown in FIG. 14 is a so-called dual spin-valve magnetic detecting element, in which a set of a nonmagnetic material layer and a pinned magnetic layer is provided at both upper and lower sides of a free magnetic layer, and is used for detecting a recording magnetic field from a recording medium, such as a hard disk.
The magnetic detecting element shown in FIG. 14 is also a CPP magnetic detecting element, in which current flows in the direction perpendicular to the surface of each layer in the multilayer laminate 9.
The magnetization of the lower pinned magnetic layer 3 is fixed in the Y direction shown in the figure and the magnetization of the upper pinned magnetic layer 7 is fixed in the direction antiparallel to the Y direction. For example, when the magnetic thickness (saturation magnetization MS×thickness t) of the second free magnetic layer 5c is larger than that of the first free magnetic layer 5a, the magnetization of the second free magnetic layer 5c when an external magnetic field is not applied is oriented to the track width direction (X direction) by a longitudinal bias magnetic field of the hard bias layers 11. Thus, the second free magnetic layer 5c is put into a single magnetic domain state, and the magnetization of the first free magnetic layer 5a is oriented antiparallel to the track width direction. The total magnetization direction of the free magnetic layer 5 is the same as that of the second free magnetic layer 5c, which has a larger magnetic thickness. When an external magnetic field is applied, the magnetizations of the first free magnetic layer 5a and the second free magnetic layer 5c are rotated with an artificial ferrimagnetic state maintained. Consequently the electric resistance of the multilayer laminate 9 is changed. An external magnetic field is detected by transforming the change in electric resistance into a change in voltage or current to draw out.
When a current is applied to a magnetic material, the specific resistance for majority conduction electrons of the magnetic material differs from that for minority conduction electrons.
The magnetic moment of a magnetic atom constituting a magnetic material is defined mainly by the orbital magnetic moments and spin magnetic moments of the electrons in the 3d or 4f orbital. In the 3d or 4d orbital of the magnetic material, the numbers of up-spin electrons and down-spin electrons are basically different from each other. One spin state of up-spin and down-spin states in which a large number of electrons in the 3d or 4f orbital are present is referred to as the majority spin, and the other state, in which a smaller number of electrons are present, is referred to as the minority spin.
On the other hand, the current flowing in the magnetic material contains substantially the same number of up-spin conduction electrons and down-spin conduction electrons. One of the up-spin and down-spin conduction electrons that is in the same spin state as the majority spin of the magnetic material are referred to as the majority conduction electrons, and the other is referred to as the minority conduction electrons.
A characteristic value β of a magnetic material is defined by the following expression:ρ↓/ρ↑=(1+β)/(1−β)(−1≦β≦1),
where ρ↓ represents the specific resistance for minority conduction electrons of the magnetic material and ρ↑ represents the specific resistance for majority conduction electrons of the magnetic material.
Hence, when β is positive (β>0), the relationship ρ↓>ρ↑ holds and majority conduction electrons flow in the magnetic material more easily than minority conduction electrons. In contrast, when β is negative (β<0), the relationship ρ↓<ρ↑ holds and minority conduction electrons flow in the magnetic material more easily.
Also, when a nonmagnetic layer is deposited on a magnetic layer, an interface resistance occurs at the interface between the magnetic layer and the nonmagnetic layer.
The interface resistance for majority conduction electrons is also different from that for minority conduction electrons.
A characteristic value γ of a combination of a magnetic material and a nonmagnetic material is defined by the following expression:r↓/r↑=(1+r)/(1−r)(−1≦γ≦1),
where r↓ represents the resistance for the minority conduction electrons at the interface between a magnetic layer and a nonmagnetic layer and r↑ represents the resistance for the minority conduction electrons of the interface.
Hence, when γ is positive (γ>0), the relationship r↓>r↑ holds and majority conduction electrons flow more easily than minority conduction electrons. In contrast, when γ is negative (γ<0), the relationship r↓<r↑ holds and minority conduction electrons flow more easily.
In the magnetic detecting element shown in FIG. 14, the lower pinned magnetic layer 2, the first free magnetic layer 5a, the second free magnetic layer 5c, and the upper pinned magnetic layer 7 generally are formed of CoFe, which is a magnetic material, and CoFe exhibits a positive β. Hence, majority conduction electrons easily flow in the lower pinned magnetic layer 3, the first free magnetic layer 5a, the second free magnetic layer 5c, and the upper pinned magnetic layer 7.
Both the nonmagnetic material layers 4 and 6 are formed of Cu. In this instance, the γ values of the interfaces between the nonmagnetic material layer 4 and the pinned magnetic layer 3, between the nonmagnetic material layer 4 and the first free magnetic layer 5a, between the nonmagnetic material layer 6 and the second free magnetic layer 5c, and between the nonmagnetic material layer 6 and the pinned magnetic layer 7 are all positive.
The nonmagnetic interlayer layer 5b is formed of Ru. In this instance, both the γ values of the interfaces between the first free magnetic layer 5a and the nonmagnetic interlayer 5b and between the second free magnetic layer 5c and the nonmagnetic interlayer 5b are negative.
FIG. 15 illustrates the relationships between β and γ values and the magnetic layers. FIG. 15 schematically shows layers involved in a magnetoresistance effect of the magnetic detecting element shown in FIG. 14. The arrows shown in the lower pinned magnetic layer 3, the first free magnetic layer 5a, the second free magnetic layer 5c, and the upper pinned magnetic layer 7 designate their magnetization directions. In the magnetic layers in which the magnetization is oriented rightward (Y direction) shown in the figure, the majority spin is in an up-spin state. In the magnetic layers in which the magnetization is oriented leftward, the majority spin is a down-spin state. The magnetization directions of the first magnetic layer 5a and the second magnetic layer 5c shown in the figure are those when the magnetic detecting element exhibits a lowest resistance.
In order to increase the change in resistance (ΔR) of the magnetic detecting element, it is preferable when the magnetization of the free magnetic layer 5 is oriented as shown in FIG. 15 that all the resistances for the up-spin conduction electrons of the magnetic layers be lower than those for the down-spin conduction electrons, and that all the interface resistances for the up-spin conduction electrons of the interfaces of the magnetic layers with the nonmagnetic layers (the nonmagnetic material layer 4 and 6 and the nonmagnetic interlayer 5b) be lower than those for the down-spin conduction electrons. Alternatively, it is preferable that all the resistances for the down-spin conduction electrons of the magnetic layers be lower than those for the up-spin conduction electrons, and that all the interface resistances for the down-spin conduction electrons of the interfaces of the magnetic layers with the nonmagnetic layers be lower than those for the up-spin conduction electrons.
However, FIG. 15 suggests that the resistances for up-spin conduction electrons of the pinned magnetic layer 3 and first free magnetic layer 5a, in which the majority spin is up and β is positive, are lower, and that the resistance for up-spin conduction electrons of the second free magnetic layer 5c and pinned magnetic layer 7, in which the majority spin is down and β is positive, are higher.
Also, the interface resistances for up-spin conduction electrons at the interfaces between the nonmagnetic material layer 4 and the pinned magnetic layer 3, between the nonmagnetic material layer 4 and the first free magnetic layer 5a, and between the second free magnetic layer 5c and the nonmagnetic interlayer 5b are lower than those for down-spin conduction electrons. In contrast, the interface resistances for up-spin conduction electrons at the interfaces between the first free magnetic layer 5a and the nonmagnetic interlayer 5b, between the nonmagnetic material layer 6 and the second free magnetic layer 5c, and between the nonmagnetic material layer 6 and the pinned magnetic layer 7 are higher than those for down-spin conduction electrons.
Thus, in the known magnetic detecting element, the conduction electron flow has not been efficiently controlled.